Measurement of road roughness

ABSTRACT

The present invention relates to a method and apparatus for measuring roughness along a surface (II) of a road or an airport runway in the driving direction. A long bar (I) has a number of ultrasound transducers (1-17) directed down toward the surface (II) of the road. The bar (I) is located e.g. in a carriage trailing behind a vehicle, at a suitable distance (for instance 20 cm) above the road surface (II). During motion, ultrasound pulses are simultaneously emitted form all transducers (1-17) for a subsequent recording of echoes from the road surface (II) with the same transducer, in order to obtain a recording of the distance between the bar and the road surface for each particular transducer. The measurement is repeated when the bar (I) has moved a distance equal to an integral multiple of the distance between two neighboring transducers, in such a manner that a number of the previously measured spots are measured once more, i.e. an overlap technique is used. The measurements are recorded in the vehicle and are data processed at a later time for presentation of e.g. an elevation profile along the completed drive distance measured.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus for measuringroughness along the surface of a traffic area, e.g. a road or an airportrunway.

More specifically, the invention concerns measuring the longitudinaldimension of the road, i.e. along a "wheel track", and not transverse tothe road (for instance in order to measure the transverse profile of thewheel track).

2. State of the Prior Art

Previously known techniques for measuring roughness or evenness along aroad track mainly comprise mechanical sensing techniques. During recentyears optical techniques have also been put into use. For example, U.S.Pat. No. 4,653,316 discloses a vehicle comprising two attached laserdevices longitudinally spaced in relation to each other, which devicesemit light beams perpendicularly down towards the road surface. Thelight spots are read by corresponding detectors (focus detection).

U.S. Pat. No. 4,685,806 discloses a system in which stationary lasersources generate vertical and horizontal laser planes as a reference fora vehicle, which vehicle is equipped with "laser cameras" or the like,i.e. a transverse row of lasers/detectors or possibly ultrasoundtransducers directed down towards the road surface. A two-dimensionaltype mapping along the road track is thereby achieved, but the use ofadditional lasers for defining e.g. a horizontal plane is expensive andtime-consuming.

SUMMARY OF THE INVENTION

The present invention utilizes only one single row of ultrasoundtransducers, which feature involves cost savings in relation to laserdevices. Furthermore, the requirement for fixed reference planes iseliminated when the present invention is put into use, and themeasurements can be made quickly and reliably.

In accordance with the present invention, this is achieved by adopting amethod for measuring surface roughness along a longitudinal dimension ofa traffic area, e.g. along a road. In the method a measuring apparatusis carried during use by a vehicle or a carriage trailing behind avehicle, wherein control means (or control), an energizing means (orenergizer) and a recording means (or a recorder) for executing themeasurements, as well as measuring devices for trailer/vehicle speed anddistance tranvelled, are brought along. The method is characterized inthat during motion there are simultaneously emitted ultrasound wavesdown toward the surface of the traffic area from a number N>2 ofultrasound transducers being located in a row on the underside of andalong a straight bar which is arranged substantially parallel to theroad surface on the trailer/vehicle and in a longitudinal direction. Theultrasound transducers are mounted an equal distance x between every twosuccessive transducers, and each transducer receives an ultrasound echofrom the surface which is due to that transducer's own emission.

Preferably the method is also characterized in that the measurements areconstantly repeated during motion in such a manner that a new ultrasoundwave emission is made when the trailer/vehicle has advanced a distancenx in relation to the preceding measurement, n being an integer andn<N-1, so that an overlap with the preceding measurement is achieved.

According to another favourable feature of the present invention, thesuccessive measurements made during motion are chained together aftertheir recording by means of a pre-programmed computer to create acontinuous elevation profile of the longitudinal dimension of thetraffic area.

Preferably the ultrasound transducers are also tested for correctfunctioning by means of an automatically controlled comparison ofmeasurement results at corresponding positions by overlap measurements.

The invention also relates to an apparatus for measuring surfaceroughness along the longitudinal dimension of the traffic area adaptedto be placed in the vehicle/trailer, and comprising control means,energizing means and recording means for the measurements, as well asmeasuring devices for the trailer/vehicle speed and distance travelled.The apparatus is characterized by a straight bar arranged in thetrailer/vehicle substantially parallel to the road surface and in thelongitudinal direction, on the underside of and along which bar arelocated a number N>2 of ultrasound transducers in a row, with an equaldistance x between every two successive transducers, adapted forsimultaneous emission during motion of ultrasound waves down toward thesurface of said traffic area and capture of the reflected waves, eachtransducer being adapted to receive only that ultrasound echo which isdue to its own emission.

Preferably the equipment also has one further ultrasound transducerarranged on the bar for correction with regard to changes in airpressure, temperature and humidity.

Preferably the equipment is adapted for repeated emission of ultrasoundwaves during motion in such a manner that a new emission is made fromthe ultrasound transducers when the trailer/vehicle has advanced adistance nx relative to the preceding measurement, n being an integerand n<N-1, so that an overlap with the preceding measurement isachieved.

DESCRIPTION OF THE DRAWINGS

The present invention is further described below with reference to theaccompanying drawings, wherein:

FIG. 1 schematically illustrates the apparatus according to the presentinvention at a first position of use;

FIG. 2 illustrates the apparatus of FIG. 1 in a second position of theuse; and

FIG. 3 schematically illustrates the invention mounted on a vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention shall now be describe din closer detail, referring to theenclosed drawing figures. The figure show schematically a substantiallyhorizontal bar I, arranged at a suitable distance about 20 cm above aroad surface II. As an example, the bar has a length of 4 m, and in thedisclosed embodiment the bar is equipped with 17 ultrasound transducersdirected down toward the road surface. However, the number oftransducers and the bar length may of course vary within wide limits.

As a starting point, it is supposed that the bar I is arranged in aposition which is substantially parallel to the road surface andpointing in the movement direction of the vehicle/trailer on which thebar is suspended. Ultrasound waves are emitted simultaneously from alltransducers perpendicularly down toward the road surface, and thereflections which are detected give rise to signals which are recordedin recording equipment brought along. Typical parameters to be measuredcan be propagation time or phase shift for the received sound waves.Apparatus dimensions, distances and wave lengths are suitably selectedin such a manner that unwanted influence upon neighboring transducers isminimized or can be removed during signal processing. Only that part ofan ultrasound reflection passing substantially perpendicularly up to theemission transducer shall in principle be used in the measurement. Thepropagation velocity of the ultrasound waves is that much higher thanthe current driving velocities of the vehicle/trailer with the bar thatno problems arise due to the fact that the transducers move while theultrasound waves are in transit between the bar and the road surface.The distance between the transducers is 25 cm in the example shown. Thusthe distance between the road surface and the 17 ultrasound transducersis measured simultaneously for all transducers while the bar is moving.In this way the apparatus can be used as an "automated straight edge". Acalculation program may later convert the recorded data in such a mannerthat maximum sag is computed when the bar "touches" the surface in two("touching is here only supposed to mean that those two positions inwhich the shortest distances are measured between bar and road surface,are used as a starting point).

As shown in FIG. 3, an energizer for energizing the measuring apparatus,a control for controlling the measuring apparatus and a recorder forrecording the measurement made by the measuring apparatus are provided.

The vehicle or trailer moves all the time towards the right side of thefigure. A new measurement is made by simultaneous emission of ultrasoundwaves from all transducers when the bar is located at a distance to theright of the starting position, which is an integral multiple of thedistance between two successive transducers. In the exemplifiedembodiment the distance from one transducer to the next one is 25 cm,and the interval between two successive measurements has been chosen tobe equal to 4×25 cm=1 m. The choice of such a measuring interval is madetaking into consideration both the wish for high accuracy, which impliesa large degree of overlap, i.e. short intervals, and a fastaccomplishment of measuring a long road distance, which implies anincreased driving speed, requiring longer recording intervals. In theexample shown, with intervals of 1 m, the practical maximum drivingspeed is in the area 40 km per hour. The overlap recording techniquedescribed above forms a basis for chaining together successiverecordings by means of a computer into a continuous elevation profile ofthe surface, given in the form of computed "elevations" with a spacingequal to the fixed mutual spacing between the ultrasound transducers.The computed elevation values do not represent the real elevation abovesea level, but can be used in order to describe irregularities with awavelength up to 50 m. The computed elevation profile forms a basis forcalculating different roughness indexes for the road surface.

The overlap measurements are also used in order to check that alltransducers are working correctly. The overlapping part of the profilefrom two successive recordings must be identical (at least afterexecuting corrections for a possible slanting of the whole bar relativeto the foregoing recording), and this fact can be used to investigate ifall transducers have been calibrated correctly. In the same manner it isalso possible to study the accuracy of the measurements and how theaccuracy is influenced by the texture of the road surface.

I claim:
 1. A method for measuring the roughness of a surface,comprising:providing a measuring apparatus with a vehicle for movementtherewith, and further providing a control means for controlling saidmeasuring apparatus, an energizing means for energizing said measuringapparatus and a recording means for recording measurements made by saidmeasuring apparatus, wherein said measuring apparatus comprises astraight bar arranged substantially parallel to the surface and in alongitudinal direction having a number N>3 of ultrasound transducerslocated in a row therealong and on the underside thereof, saidultrasound transducers being mounted with an equal distance x betweenevery two successive said transducers; moving the vehicle along thesurface such that said bar moves in the longitudinal direction andsimultaneously emitting ultrasound waves down toward the surface fromsaid number of ultrasound transducers; and receiving with each saidtransducer an ultrasound echo from the surface due that said ultrasoundtransducer's own ultrasound wave emission.
 2. The method of claim 1, andfurther comprising:repeating said emission and reception of ultrasoundwaves during movement of the vehicle each time the vehicle travels adistance nx relative to the location of the preceding said emission andreception, n being an integer preceding said emission and reception, nbeing an integer and n>N-1, such that the repeated said emission andreception overlaps with the preceding said emission and reception. 3.The method of claim 2, wherein n<N-2.
 4. The method of claim 2, whereinsuccessive said emissions and receptions are recorded by said recordingmeans and chained together by a preprogrammed computer into a continuouselevation profile of the longitudinal dimension of the surface.
 5. Themethod of claim 4, wherein said ultrasound transducers are checked forcorrect functioning by automatically controlled comparison of theresults of said emissions and receptions at corresponding overlappositions of said ultrasound transducers.
 6. The method of claim 2,wherein said ultrasound transducers are checked for correct functioningby automatically controlled comparison of the results of said emissionsand receptions at corresponding overlap positions of said ultrasoundtransducers.
 7. An apparatus for use with a vehicle for measuring theroughness of a surface, comprising:a straight bar adapted to be arrangedsubstantially parallel to the surface in a longitudinal direction formovement with the vehicle; and a number N>3 of measuring means forsimultaneously emitting ultrasound waves during movement of the vehiclein the longitudinal direction down toward the surface and receiving onlytheir respective reflected ultrasound wave echoes produced by their ownemission, said number of measuring means being arranged in a row alongthe underside of said straight bar with an equal distance x betweenevery two successive said measuring means, and a control means forcontrolling said number of measuring means, an energizing means forenergizing said measuring means and a recording means for recordingmeasurements made by said measuring means in the form of emissions andreceptions of said ultrasound waves.
 8. The apparatus of claim 7,wherein each said measuring means comprises an ultrasound transducer. 9.The apparatus of claim 8, and further comprising correction means onsaid bar for providing corrections with regard to changes in airpressure, temperature and humidity.
 10. The apparatus of claim 9,wherein said correction means comprises an additional ultrasoundtransducer.
 11. The apparatus of claim 10, wherein said number ofmeasuring means, said control means and said energizing means areadapted for repeating the emission of ultrasound waves during motion ofthe vehicle such that a new emission and reflection are made from saidnumber of measuring means when said straight bar has advanced a distancenx relative to the point of the preceding simultaneous emission andreception of ultrasound waves, n being an integer and n<N-1, such thatthe repeated simultaneous emission and reception overlaps with thepreceding simultaneous emission and reception.
 12. The apparatus ofclaim 11, wherein n<N-2.
 13. The apparatus of claim 7, wherein saidnumber of measuring means, said control means and said energizing meansare adapted for repeating the emission of ultrasound waves during motionof the vehicle such that a new emission and reflection are made fromsaid number of measuring means when said straight bar has advanced adistance nx relative to the point of the preceding simultaneous emissionand reception of ultrasound waves, n being an integer and n<N-1, suchthat the repeated simultaneous emission and reception overlaps with thepreceding simultaneous emission and reception.
 14. The apparatus ofclaim 13, wherein n<N-2.